Method for manufacturing tempered glass sheet and apparatus for manufacturing the same

ABSTRACT

A gas is supplied to the surface of the glass sheet transferred between a heating furnace and a cooling apparatus for tempering the glass sheet. The gas is supplied from the upstream side with respect to the direction of transfer of the glass sheet by an air curtain device. This gas runs along the glass sheet surface (upper surface) downstream with respect to the direction of transfer to obstruct the flow of cooling gas from the cooling apparatus in the upstream direction. The gas prevents cooling air from the cooling apparatus from invading the heating furnace so that the difference of the curvature of the glass sheet on the front and rear part can be eliminated.

FIELD OF THE INVENTION

This invention relates to a method for manufacturing a tempered glasssheet and an apparatus thereof. More particularly, this inventionrelates to a method and an apparatus for manufacturing a tempered glasssheet useful for architecture, automobiles or the like.

BACKGROUND OF THE INVENTION

As the window glass sheet for architecture or automobile, a temperedglass sheet is extensively used as a safety glass sheet. As a method formanufacturing a tempered glass sheet, there is extensively practiced anair-cooling method of quickly cooling the glass sheet that has beenheated to a temperature near the softening point to form a compressivestress layer in the surface of the glass sheet.

In view of the design and aerodynamic characteristics of automobiles,there are great demands for curved window glass sheets. Accordingly, inthe air-cooling method the heated glass sheet is often formed into acurved shape before the glass sheet is cooled to temper. The method forbending a glass sheet includes a method of pressing a glass sheetsuspended by a tong (a glass-suspender) with a pair of convex andconcave press molds, and a method of pressing a glass sheet that hasbeen transferred horizontally from a heating furnace with a pair ofupper and lower press molds.

In the bending methods involving pressing with molds, the step ofheating a glass sheet and the step of bending the glass sheet arebasically taken as independent steps. However, there is proposed amethod to practice the two steps as a single step. In such a method theglass sheet transferring means such as rolls or beds are provided in theheating furnace with a predetermined curvature, so that the heated glasssheet is gradually bent down by its own weight until it constitutes acurved surface having the curvature. The bent glass transferred to thecooling apparatus adjacent to the heating furnace is cooled into atempered glass sheet. This method is excellent in the point that thereis no necessity to press the glass sheet individually. In order to makeuse of this feature, various improvements on the method have been madefor practical applications (e.g., Japanese Examined Patent PublicationsNos. S44-14832/1969, S48-5242/1973, and Japanese Unexamined PatentPublication No. H7-237928/1995).

However, the tempered glass sheet by the method tends to be formed intoa shape different from what originally was expected. Typically, as shownin FIG. 5A, when a flat tempered glass sheet is expected, the rear endpart of the glass sheet in the direction of transfer becomes convex, andas shown in FIG. 5B, when a curved glass sheet that should show a convexupward shape was expected, the rear end part shows a larger curvaturethan the front end part in the direction of transfer.

Such a difference of curvature is caused mainly by the fact that thecooling air blown to the glass sheet in the cooling apparatus goes intothe heating furnace. In other words, as shown in FIG. 6, when the glasssheet is transferred to the cooling apparatus, the cooling air blown tothe upper surface of the front end part in the direction of transfer ofthe glass sheet runs along the surface of the glass sheet to theupstream side of transfer to go into the heating furnace. The coolingair lowers the temperature on the upper surface at the rear end part ofthe glass sheet before it reaches the cooling apparatus. On the otherhand, the lowering of the temperature on the upper surface at the frontend part of the glass sheet is not so remarkable as at the rear end partof the glass sheet, because the intrusion of the cooling air into theheating furnace becomes remarkable by the flow along the surface of theglass sheet, as shown in FIG. 6.

As a result, at the rear end part of the glass sheet in the direction oftransfer, the temperature variation range in cooling becomes greatlydifferent between the upper and the lower surfaces of the glass sheetand the shrinkage amounts by cooling also show differences. Thus, therehas been a phenomenon that the curvatures of the glass sheet becomedifferent between the front end part and the rear end part in thedirection of transfer.

In view of the above problem, in Japanese Utility Model Publication No.H4-41152/1992, there is proposed to dispose a heating device between theheating furnace and the cooling apparatus. According to the heatingdevice, the inconvenience as referred to above can be alleviated bycompensating the temperature difference on the surface of the glasssheet prior to it being transferred into the cooling apparatus. However,the method using the heating device necessitates heating a specifiedpart of the glass sheet in the course of transferring it, so that theoperation is not necessarily easy, and involves a problem to beovercome.

SUMMARY OF THE INVENTION

An object of the present invention is, in the light of the situation asdescribed above, to provide a method and an apparatus for manufacturinga tempered glass sheet which can suppress simply and assuredly thedifference of the curvatures of the glass sheet that result between thefront end part and the rear end part in the direction of transport.

According to the present invention, there is provided a method formanufacturing a tempered glass sheet, which comprises heating a glasssheet in a heating furnace, transferring the glass sheet from theheating furnace to a cooling apparatus adjacent to the heating furnace,cooling the glass sheet in the cooling apparatus with a cooling air soas to temper the glass sheet, and supplying a gas onto the surface ofthe glass sheet transferred from the heating furnace to the coolingapparatus so that the gas runs along the surface in the downstreamdirection of transferring the glass sheet.

According to the present invention, there is provided another method formanufacturing a tempered glass sheet, which comprises heating a glasssheet in a heating furnace, transferring the glass sheet from theheating furnace to a cooling apparatus adjacent to the heating furnace,cooling the glass sheet in the cooling apparatus with a cooling air soas to temper the glass sheet, and supplying a gas onto the surface ofthe glass sheet from the upstream side of transferring the glass sheetfurther than the surface so as to suppress intrusion of the cooling airinto the heating furnace.

According to the above methods, it is possible to suppress effectivelythe difference of the shape between the front end part and the rear endpart in the direction of transfer of the glass sheet. This is becausethe cooling air from the cooling apparatus that tends to invade theheating furnace along the surface of the glass sheet is prevented fromrunning in the direction of the heating furnace by the gas which issupplied to the surface of the glass sheet.

The above method can be carried out by an apparatus for manufacturing atempered glass sheet, which comprises a heating furnace for heating aglass sheet having a transfer outlet for the glass sheet, a coolingapparatus for cooling the glass sheet with a cooling air so as to temperthe glass sheet and having a transfer inlet disposed to be adjacent tothe transfer outlet of the heating furnace, carrying means fortransferring the glass sheet from the heating furnace to the coolingapparatus through the transfer outlet and the transfer inlet, and gasblowing means positioned upstream of the cooling apparatus and arrangedso as to blow a gas onto a surface of the glass sheet located at aposition downstream of the position of the gas blowing means.

According to the apparatus for manufacturing a tempered glass sheet, itis possible to suppress effectively the difference of the curvaturesbetween the front end part and the rear end part in the direction oftransfer of the glass sheet and produce a tempered glass having areduced difference from the expected configuration. This is because thecooling air from the cooling apparatus that tends to invade the heatingfurnace along the surface of the glass sheet is prevented from runningin the direction of the heating furnace by the gas supplied to thesurface of the glass sheet. Furthermore, according to this productionapparatus, a partial difference of curvatures of the sheet glass can besuppressed simply and assuredly without requiring a large remodeling forthe conventional apparatus already in use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an embodiment of the productionequipment of the present invention.

FIG. 2 is a view showing an embodiment of the air curtain device to beused for the production equipment of the present invention.

FIG. 3 is a sectional view showing another embodiment of the productionequipment of the present invention.

FIG. 4 is a sectional view showing a still further embodiment of theproduction equipment of the present invention.

FIG. 5A is a perspective view showing a glass sheet that has differentcurvatures on the front and rear part in the direction of transfer, andFIG. 5B is a perspective view showing another glass sheet that has thedifferent curvatures.

FIG. 6 is a sectional view showing an embodiment of the productionapparatus for the bent and tempered glass sheet in conventional use.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the method for manufacturing a tempered glass sheet as describedabove, a gas may be supplied from the position in between the heatingfurnace and the cooling apparatus, but it is preferable for the gas tobe supplied from the inside of the heating furnace. Also, irrespectiveof the position of supplying the gas, it is preferable to supply a gasheated in the heating furnace. According to these preferred embodiments,the high temperature gas in the heating furnace is to be supplied to theglass sheet surface, and, when compared, for example, with the case ofsupplying a gas at about room temperature, it is possible to suppressthe lowering of the temperature on the upper surface of the glass sheetbefore being carried to the cooling apparatus, and it becomes possibleto alleviate the temperature difference per se on the upper and lowersurfaces of the tempered glass sheet, and to improve the precision offorming the tempered glass sheet.

Furthermore, in the above method for manufacturing the tempered glasssheet, a gas may be supplied to the glass sheet surface at a position inthe vicinity of the heating furnace transfer outlet or in between theheating furnace and the cooling apparatus. It is preferable to supply agas to the neighborhood of the position of the upstream end of the areain which the cooling air is supplied to the glass sheet. The position onwhich the gas is supplied is more preferably approximately the sameposition as that stated in the above. According to these preferredexamples, the time during which the supplied gas is in contact with theglass surface is lessened, and the temperature decrease on the uppersurface of the glass sheet prior to the cooling process can besuppressed, so that, in the same manner as described above, the formingprecision of the tempered glass sheet can be improved.

Furthermore, in the method for manufacturing the tempered glass sheet asdescribed above, it is preferable to subject the glass sheet to bendforming in the heating furnace. It is because the present inventionmethod is particularly effective for improving the precision of shape ofthe bend tempered glass. This bend forming is preferably that made byutilizing the deformation of the heated glass sheet by own weight.

Hereinafter, preferred embodiments of the present invention aredescribed with reference to the drawings.

(First Embodiment)

FIG. 1 is a sectional view showing an example of the glass sheettempering apparatus of the present invention. In the heating furnace 1,there is provided an air table 11 as the means for transferring a glasssheet. This air table 11 has a large number of nozzle holes, so that theheated air blown out from the nozzle holes jets out to the lower surfaceof the glass sheet to support the glass sheet for transfer. This hot air12 takes part in transferring the glass sheet while floating and inheating the glass sheet to soften it. The glass sheet to be bend-formedis heated to a temperature range in the vicinity of the softening point(preferably at more than the stress point and lower than the softeningpoint) to have a certain curvature along the surface configuration ofthe air table under dead weight.

The air table typically has a curvature in a direction perpendicular tothe direction of transfer of the glass sheet and is shaped to be convexupward, but it may have a shape to be convex downward, and the desiredtempered glass may be a flat sheet form if the objective tempered glassis a flat sheet. Alternatively, a roll or the like may be used in placeof the air table 11, as the means for transferring the glass sheet.

The transfer outlet of the heating furnace is preferably slightly largerthan the thickness of the glass sheet, in consideration of the heatingefficiency and entry of external air into the heating furnace. Inpractice, it is required to secure a space to a degree that the contactof the heated glass sheet can be prevented. The space defined by thetransfer outlet is divided into the upper and lower spaces by the glasssheet while it passes through the outlet. Of these spaces, what providesthe problem in the entry of the cooling air is a space on the upper partof the glass sheet. The space underneath the glass sheet is narrow underthe effect of the dead weight of the glass sheet, and in addition, asthe air which blows out from the air table plays the role of the aircurtain, the entry of the cooling air is substantially of no problem.

Inside the cooling apparatus 2 installed on the downstream side oftransfer adjacent to the heating furnace 1, there are disposed aplurality of quench modules 21, 22 directed towards the glass sheettransfer route from upper and lower positions. By the air (typically,cooling air) supplied from these quench modules 21, 22, the glass sheetis quenched and tempered while being transferred. The quench modules 21,22 are not limited to be of the configurations shown in FIG. 1 but maybe tubular or the like.

From the viewpoint of improving the glass sheet strength, the heatingfurnace 1 and the cooling apparatus 2 are preferably disposed nearbyeach other.

Above the glass sheet transfer route between the heating furnace and thecooling apparatus 2, there is installed an air curtain device 3. Thisair curtain device 3 is, as shown in FIG. 2, preferably a hollow pipehaving a plurality of nozzle holes 31 arranged in a row in thelengthwise direction (the widthwise direction with respect to the glasssheet). Of course, the gas discharge port of the air curtain device 3need not necessarily be plural nozzle holes independent from one anotherbut may be a slit which extends in the lengthwise direction. The aircurtain device 3 may have a circular or elliptical cross section asshown in FIG. 2, but without specially limitation, and the section maybe other shapes such as rectangular.

Each nozzle hole 31 is disposed so that the gas can be dischargedobliquely downward in a downstream direction with respect to thetransfer of the glass sheet. Each nozzle hole 31 is preferably disposedto jet out a gas in the direction inclined obliquely downward in thedownstream direction with an inclination in the range of 30 to 60degrees from vertical. According to this preferred embodiment, the gasrunning downstream on the glass sheet surface in the direction oftransfer of the glass sheet can be supplied in a stabilized state.

Furthermore, as shown in FIG. 2, if the glass sheet is bend-formed in aheating furnace, it is preferable for the air curtain device 3 to have acorresponding configuration, preferably for example an upwardly curvedconvex shape as shown in FIG. 2.

The position for setting the air curtain device 3 is preferably at aheight of 10 mm-120 mm from the upper surface of the glass sheet.According to this preferred embodiment, there is no apprehension for theair curtain device 3 to come into contact with the softened glass sheet,and yet the intrusion of the cooling air into the heating furnace fromthe cooling apparatus can be effectively suppressed.

The hole diameter of the nozzle holes 31 of the air curtain device 3 ispreferably 1.0-2.0 mm, and the pitch of the nozzle holes is preferably10 mm-20 mm. According to these preferred examples, entry of the coolingair blown at high pressure can be securely prevented by the "aircurtain" formed by the gas jetting out from the nozzle holes.

Next, an example of the method for manufacturing the tempered glasssheet using this apparatus is explained.

The glass sheet which is heated in the heating furnace 1 and bend-formedby utilizing the dead weight of the glass sheet is passed through theglass transfer outlet of the heating furnace 1 and transferred to thecooling apparatus. When the front end part of the transferred glasssheet approaches the cooling apparatus 2 and cooling air from thecooling modules 21, 22 comes to be blown onto the surface of the frontend part, the cooling air tends to run upstream with respect to thedirection of transfer along the upper surface of the glass sheet.However, as the gas from the air curtain device 3 has already beensupplied to the upper surface of the glass sheet and said gas has run tothe downstream with respect to the transfer direction along the uppersurface of the glass sheet, the flow of the cooling air to the upstreamside is obstructed, and the intrusion of the cooling air into the insideof the heating furnace is suppressed.

Ordinarily, in order to improve productivity, a plurality of glasssheets are continuously supplied to the tempering apparatus, and therespective sheet is bend-formed according to necessity, and transferredfrom the heating furnace 1 to the cooling apparatus 2, in which it isquenched to be tempered. In order to meet the glass sheet which comes tobe continuously transferred, cooling air is continuously supplied in thecooling apparatus 2. Accordingly, it is desirable for the gas from theair curtain device 3 to be continuously supplied.

Moreover, in order to suppress effectively the intrusion of the outsidegas into the heating furnace, the discharge pressure of the gas suppliedfrom the air curtain device 3 can be 0.02 kg/cm² -3 kg/cm². This isbecause, when the discharge pressure is too low, it becomes difficult toobstruct intrusion of cooling air, and when it is too high, there is anapprehension that the stabilized transfer of the glass sheet could becompromised. Especially, when the discharge pressure is increased, thereis a likelihood for the discharge gas from the air curtain device 3 tocause springing up of the rear end of the glass sheet after passage ofthe glass sheet to hamper the stabilized transfer of the glass sheet.Therefore, when importance is attached to such a point, the dischargepressure of the gas is more preferably no more than 2 kgf/cm².

(Second Embodiment)

FIG. 3 is a sectional view showing another embodiment of the glass sheettempering apparatus of the present invention. This apparatus is commonwith the apparatus shown in FIG. 1 with respect to the basicconstitution of the heating furnace 1 and the cooling device 2, but isdifferent in the point that an air curtain device 3 is disposed insidethe heating furnace 1.

According to the apparatus shown in FIG. 3, the gas blown out from theair curtain device 3 is to be supplied to the upper surface of the glasssheet while involving the high temperature gas in the heating furnace.Accordingly, when a gas is supplied from the air curtain device 3 by theapparatus shown in FIG. 3, intrusion of the cooling air into the heatingfurnace is suppressed in the same manner as in the first embodiment, andthe lowering of temperature on the upper surface of the glass sheet bythe supplied gas is more suppressed and the temperature differencebetween the upper and the lower surfaces of the glass sheet becomessmaller than in the case of the first embodiment.

Since the temperature difference between the upper and the lowersurfaces of the glass sheet to be transferred into the cooling apparatusgives differences in shrinkage rate between the upper and the lowersurfaces, the second embodiment is more preferable from the viewpoint offorming the glass sheet to a predetermined shape (shape formed in theheating furnace).

The embodiment for supplying a heated gas in the heating furnace is notlimited to the embodiment shown in FIG. 3 but may be to supply a gasthrough the vent pipe or the like from the heating furnace to thecurtain device as shown in FIG. 1 for example.

(Third Embodiment)

FIG. 4 is a sectional view showing another embodiment of the glass sheettempering apparatus of the present invention. This apparatus is commonwith the apparatus shown in FIG. 1 with respect to the basicconstitution of the heating furnace 1 and the cooling device 2, but isdifferent in the point that an air curtain device 3 is disposed in thevicinity of the cooling apparatus.

According to the apparatus shown in FIG. 4, the gas blown out obliquelydownward from the air curtain device 3 comes into contact with the uppersurface of the glass sheet at approximately the same position as orslightly upstream of the cooling air blown out in an approximatelyvertical direction from the cooling module disposed furthest upstream inthe cooling apparatus. This gas suppresses intrusion of the cooling airinto the heating furnace in the same manner as in the first embodiment.

On the other hand, because the time during which the gas supplied fromthe air curtain is in contact with the glass sheet is extremely short,the temperature on the surface of the glass sheet to be transferred tothe cooling apparatus does not become lower than the case shown in thefirst embodiment, and it is possible to improve the molding precision ofthe glass sheet in the same manner as in the second embodiment.

In the second and third embodiments, basically it is preferable to adoptthe gas discharge pressure, installation position of the air curtaindevice, and size and arrangement of the nozzle hole as described in thefirst embodiment.

When the air curtain device is fitted to both of the positions shown inFIG. 3 and in FIG. 4 so as to supply a gas to the surface of the glasssheet from both air curtains, the forming precision of the glass sheetcan be improved to a degree that is entirely of no problem.

Further, in practicing the present invention method, as described above,ordinarily, during the transfer of a sheet of glass sheet from theheating furnace to the cooling apparatus, a gas is incessantly suppliedto the glass sheet surface from the air curtain device. Alternatively,the gas may be jetted only to a predetermined portion in the glass byopening or closing the solenoid valve provided on the intermediate partof the piping for supply of gas to the air curtain device.

According to this method, by positively utilizing the surfacetemperature decrease of the glass sheet by intrusion of the cooling airinto the heating furnace or by blowing of gas, it becomes possible togive the intended curvature to the glass sheet in the transferdirection.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not restrictive, the scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A method for manufacturing a tempered glasssheet, comprising:transferring a glass sheet heated in a heating furnacefrom the heating furnace to a cooling apparatus adjacent to the heatingfurnace; and cooling the glass sheet in the cooling apparatus with acooling air so as to temper the glass sheet; wherein a gas is heated inthe heating furnace and supplied onto a surface of the glass sheettransferred from the heating furnace to the cooling apparatus so thatthe gas runs along the surface of the glass sheet in a downstreamdirection with respect to the transferring of the glass sheet, and thegas is supplied between the heating furnace and the cooling apparatus ina vicinity of a position furthest upstream of a region in which thecooling air is blown onto the glass sheet.
 2. A method for manufacturinga tempered glass sheet according to claim 1, wherein the glass sheet isformed into a curved shape in the heating furnace due to the self-weightof the glass sheet.
 3. A method for manufacturing a tempered glass sheetaccording to claim 1, further comprising a step of heating the glasssheet nearly to a softening point of the glass sheet in the heatingfurnace.
 4. A method for manufacturing a tempered glass sheet,comprising:transferring a glass sheet heated in a heating furnace fromthe heating furnace to a cooling apparatus adjacent to the heatingfurnace; and cooling the glass sheet in the cooling apparatus with acooling air so as to temper the glass sheet; wherein a gas is suppliedonto a surface of the glass sheet from upstream of the surface withrespect to the direction of transferring the glass sheet so as tosuppress intrusion of the cooling air into the heating furnace, and thegas supplied is heated in the heating furnace.
 5. A method formanufacturing a tempered glass sheet according to claim 4, wherein thegas is supplied between the heating furnace and the cooling apparatus ina vicinity of a position furthest upstream of a region in which thecooling air is blown onto the glass sheet.
 6. A method for manufacturinga tempered glass sheet according to claim 4, wherein the glass sheet isformed into a curved shape in the heating furnace due to the self-weightof the glass sheet.
 7. A method for manufacturing a tempered glass sheetaccording to claim 4, further comprising a step of heating the glasssheet nearly to a softening point of the glass sheet in the heatingfurnace.